1. Field of the Invention
The present invention generally relates to a plasma display panel (PDP), and more particularly to a color plasma display panel in which a white color temperature is increased based on improvements of sustain electrodes.
2. Description of the Related Art
Recently, in the field of display apparatuses, a complexity of information to be displayed, a size of a display panel and a definition of a display panel are increasing rapidly. Therefore, an improvement of a display quality of a PDP is required. The PDP is being developed at a rapid pace because the PDP has advantageous characteristics, for example, no-flicker, ease of achieving a large panel, a high brightness and a long lifetime. There are two types of AC-PDPs. One type has two electrodes which create a selection-discharge (an address-discharge) and a sustain-discharge between the two electrodes. The other type has three electrodes, the third electrode of which creates address-discharges. In a gray-scale color PDP, the phosphors placed in discharge-cells are excited by an ultraviolet light generated by discharges. The phosphors are degraded by ionic bombardments simultaneously generated by the discharges. In the PDP having two electrodes, the phosphors are directly bombard by the ions. This may results in a short lifetime of the phosphors. To avoid the short lifetime of the phosphors, three electrodes generating a surface discharge are generally used in the color PDP. There are types of PDPs having the three electrodes. One type has the third electrode on the same substrate as that on which the first and the second electrodes are provided and the other type has the third electrode on a separate substrate which is opposite to the substrate having the first and the second electrodes. There are two types of PDPs having the three electrodes provided on the same substrate. One type has the third electrode deposited on the first and the second electrodes and the other type has the third electrode deposited under the first and the second electrodes. Furthermore, in a transmission type PDP, a light emitted from the phosphor can be seen through the phosphor, and in a reflection type PDP, a light reflected from the phosphor can be seen. Discharge cells are separated from adjacent discharge cells by separators. Each discharge cell may be sealed by surrounding separators. Otherwise, separators may be provided in only one direction of each discharge cell and each cell is isolated in another direction by an action of an electric field generated by proper gaps between the electrodes.
FIG. 1 shows a plan view of a PDP of one example according to the prior art. Two sustain electrodes, such as an X-electrode 101 (the first electrode) and Y-electrodes 102 to 106 (the second electrodes) are deposited on a substrate. Address electrodes 107 to 116 (the third electrodes) are provided on another substrate. Then, these two substrates are sealed together. Separators 117 to 127 are created perpendicular to a surface of the substrates. Separators 117 to 127 are also perpendicular to the X-electrode 101 and the Y-electrodes 102 to 106 and parallel to the address electrodes 107 to 116. Each of the X-electrode 101 and the Y-electrodes 102 to 106 has a transparent electrode in part. This PDP is the reflection-type PDP. Therefore, a light reflected from the phosphor can be seen.
FIG. 2 shows a cross section in a direction parallel to the address electrodes 107 to 116 of the PDP shown in FIG. 1. The PDP comprises a front glass substrate 201 and a rear glass substrate 202. Sustain electrodes which comprise the X-electrode and the Y-electrodes are deposited on the front glass substrate 201. The X-electrode has a transparent electrode 203 and a bus electrode 204. The Y-electrode has a transparent electrode 205 and a bus electrode 206. The transparent electrodes 203 and 205 are made up of an ITO which is a transparent conductive film of mainly indium oxide because they must transmit a light reflected from a phosphor. A resistance of the bus electrodes 204, 206 and 208 is needed to be low to prevent a voltage drop caused by the electrode resistance. Therefore, the bus electrodes 204, 206 and 208 are made up of chrome or copper. The X-electrode and the Y-electrodes are covered with a dielectric layer 209. Furthermore, a magnesium oxide protection layer 210 is provided on the dielectric layer 209. A surface of the protection layer 210 is a discharge surface. The address electrode 211 is deposited on the rear glass substrate 202 perpendicular to the X-electrode and the Y-electrodes which are deposited on the front glass substrate 201.
FIG. 3 shows a cross section in a direction parallel to the X-electrodes 101 of the PDP shown in FIG. 1. Separators 310, 311, 312 and 313 are deposited between address electrodes 307, 308 and 309. A red phosphor 314, a green phosphor 315 and a blue phosphor 316 are deposited on the address electrodes between the separators. The front glass substrate 301 and the rear glass substrate 302 are assembled so that tips of the separators 310 to 313 are sealed to a magnesium oxide layer 306.
FIG. 4 show a plan view of sustain electrodes for red, green and blue phosphors. A sustain electrode pair comprises an X-electrode 1 and a Y-electrode 1. The X-electrode 1 comprises a bus electrode 401 and a transparent electrode 402. The Y-electrode 1 comprises a bus electrode 403 and a transparent electrode 404. A sustain discharge is created at a slit 413 between the X-electrode 1 and the Y-electrode 1. This slit 413 is referred to as a positive slit 1. A slit 415 is also referred to as a positive slit 2. A sustain discharge is not created at a slit 414 between the X-electrode 2 and the Y-electrode 1. This slit 414 is referred to as an opposite slit 2. A red phosphor is deposited between separators 409 and 410 and a red light is emitted from the positive slit 1 between separators 409 and 410 when a sustain discharge is created at the positive slit 1. A green phosphor is deposited between separators 410 and 411, and a blue phosphor is deposited between separators 411 and 412. A green light and a blue light are also emitted from the positive slit 1 when a sustain discharge is created at the positive slit 1. Address electrodes not shown in FIG. 4 are provided parallel to the separators. FIG. 5 shows a relationship among a sustain electrode size, a discharge current value and a brightness. FIG. 5 (A) shows a relationship between the sustain electrode size and the discharge current value. A solid line 501 shows a case where each sustain electrode provided for the red, green and blue phosphor cells has the same width. In this case, each discharge current at the red, green and blue phosphor cells has the same value despite the sustain electrode size. As a result, each ultraviolet ray generated by a discharge to excite the red, green and blue phosphor cells has the same strength.
However, each luminous efficiency and maximum brightness of the red, green and blue phosphors are different from each other. Therefore, a brightness of a particular color is lower than those of other colors even if each phosphor is excited by the ultra violet ray having the same strength generated by the discharge having the same strength. As a result, a white color temperature is reduced and this results in a degradation of a display quality.
For example, FIG. 5 (B) shows a relationship between the sustain electrode size and the brightness. As described above, in case that each sustain electrode provided for the red, green and blue phosphor cells has the same width, the red, green and blue phosphor cells are excited by ultraviolet rays having the same strength. A blue brightness 511, a red brightness 512 and a green brightness 513 are different from each other. The blue brightness 511 is the lowest of the three. As a result, the white color temperature is low.
It is a general object of the present invention to provide a plasma display panel in which the above disadvantages are eliminated. A more specific object of the present invention is to provide a plasma display panel in which a white color temperature is increased.
The above objects of the present invention are achieved by a plasma display panel comprising plural kinds of phosphors, each of which emits a light having a different kind of color, separators which separate the plural kinds of phosphors and discharge cells having sustain electrode pairs which create discharges to create the light emissions from the phosphors. In the plasma display panel, a sustain discharge current through each sustain electrode pair in the discharge cells is set a different value according to a brightness of each light emitted from the plural kinds of phosphors.
According to the invention, a white color temperature is increased because the brightness of a particular discharge cell which is defined by the separators surrounding a discharge space in which the phosphor having a low brightness is deposited is increased.